Investigations into differences between vaccinia and myxoma virus plaquing properties identifies strategies for increasing the oncolytic efficacy of myxoma virus.

摘要

Despite both being poxviruses, vaccinia (VACV) and myxoma (MYXV) form very different plaque types. VACV plaques are large and show a central clearing of cells, while MYXV plaques are smaller and result in a clumping of cells. VACV spread is promoted by the formation of an enveloped form of virus (EV) and localized actin rearrangements (called actin tails), which push EV from a cell. Since mutations in genes that catalyze these processes often reduce VACV plaque size (i.e. mutants are more MYXV-like), we investigated the relative efficiency of these viruses to produce actin tails. MYXV forms far fewer actin tails than VACV. Bioinformatics identified MYXV counterparts to these VACV genes---minus one. MYXV lacks a F11 homolog. F11 promotes VACV spread by disrupting cortical actin through inhibition of RhoA-mDia1 signaling. We hypothesized the absence of a MYXV F11 homolog explains these plaquing differences and therefore generated a recombinant MYXV that expresses F11. This virus formed larger plaques, grew to higher levels, and induced a number of cellular morphological changes not observed in control MYXV strains. These included cell rounding, disruption of cortical actin, and more actin tails. F11+ MYXV formed smaller plaques and less actin tails than VACV, suggesting that while an absence of F11 partially explains why MYXV forms smaller plaques than VACV other differences likely exist.;MYXV naturally has oncolytic abilities, but does not spread well outside of lagomorphs, which could limit its abilities to treat cancer. We thought that enhanced spread conferred by F11 might increase MYXV's oncolytic effectiveness. F11+ MYXV showed enhanced abilities to control tumor growth and prolong survival in xenografted mice bearing human mammary tumors. This virus also spread more efficiently from an injected tumor, to a second untreated tumor. We could mimic F11's stimulatory effects on MYXV growth in cell culture by pharmacological inhibition or siRNA-mediated silencing of key regulators of the actin cytoskeleton. This suggests that chemical disruption of actin could enhance wildtype MYXV's oncolytic capacity. Since all viruses must overcome barriers to exit, like cortical actin, this approach could be used to improve the effectiveness of other oncolytic viruses.